Actin-binding proteins bind to actin and can modify its properties. You purify a

Question

Actin-binding proteins bind to actin and can modify its properties. You purify a protein, Cap1, that seems to bind and cap one end of an actin filament, although you do not know whether it binds the plus end or the minus end. To determine which end of the actin filament your protein binds to, you decide to examine the of Capl on actin polymerization by measuring the kinetics of actin filament formation in the presence and the absence of Cap1 protein. You obtain the following results (see figure below). Do you think Capl binds the or the minus end of actin? Explain your reasoning.

Explanation / Answer

Binding of actin binding proteins at the + end of actin inhibits actin polymerisation while binding of actin binding proteins at the - end prevents actin monomer dissociation.The above figure shows amount of polymerised actin with time.Since the amount of polymerised actin is less when actin is bound to cap 1 protein, we can say that cap1 protein binds to the + end of actin.

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